This invention relates to preparation of diaminodiphenyl ethers, and more particularly to preparation of bis(aminophenyl)ethers (e.g. oxydianiline) from N-acetylaminophenol compounds.
Bis(aminophenyl)ethers (hereinafter sometimes referred to collectively as BAPE's) are known to be valuable as bifunctional cross-linking and network-extending agents for polymeric resins, plastics and elastomers. There is a substantial demand by users of BAPE's for high-purity and substantially colorless commercial grade of BAPE products, especially such ODA products.
In Canadian Pat. No. 992,991 (incorporated herein by reference), Jamieson et al. described and claim inter alia a process for preparing 4,4'-diaminodiphenyl ether (also known as 4,4'-oxydianiline or simply 4,4'-ODA) which comprises refluxing a mixture containing approximately equimolar amounts of p-aminophenol (sometimes referred to as PAP), p-chloronitrobenzene, and potassium carbonate in dimethylformamide, hydrogenating the resulting mixture in the presence of a catalyst, recovering the dimethylformamide (or DMF as it is commonly referred to) by distillation, and crystallizing 4,4'-diaminodiphenyl ether (i.e., 4,4'-ODA) from the residue. As described in Example 1 of the Canadian Patent, the residue (remaining after distilling to recover 80% of the DMF) was drowned with water, filtered and reprecipitated to give crude 4,4'-oxydianiline(4,4'-ODA). Example 3 of Jamieson et al. states that, after "cooling and removal of catalyst by filtration, 4,4'-ODA was isolated as a pink solid by drowning the reaction mixture, including the DMF, with water and filtering," the pink solid having melting point (m.p.) of 187.degree.-189.degree. C. In Example 4 Jamieson et al. teach that the 4,4'-ODA "was isolated in the usual way," excess p-aminophenol was removed, the resulting "light pink product" had "m.p. 188.degree.-190.degree. C.," and "reprecipitation from n-butanol gave a nearly colorless product, m.p. 190.degree.-191.degree. C."
Although the Jamieson et al. process for preparing 4,4'-ODA represents a substantial advance, there remains a substantial need in the art for an improved process for preparing 4,4'-ODA (and other bis(aminophenyl)ethers). There also remains a need for an improved process for making high purity substantially colorless BAPE's, especially ODA.